Module aws_lambda_powertools.event_handler

Event handler decorators for common Lambda events

Expand source code 
"""
Event handler decorators for common Lambda events
"""

from .api_gateway import (
    ALBResolver,
    APIGatewayHttpResolver,
    ApiGatewayResolver,
    APIGatewayRestResolver,
    CORSConfig,
    Response,
)
from .appsync import AppSyncResolver
from .lambda_function_url import LambdaFunctionUrlResolver

__all__ = [
    "AppSyncResolver",
    "APIGatewayRestResolver",
    "APIGatewayHttpResolver",
    "ALBResolver",
    "ApiGatewayResolver",
    "CORSConfig",
    "LambdaFunctionUrlResolver",
    "Response",
]

Sub-modules

aws_lambda_powertools.event_handler.api_gateway
aws_lambda_powertools.event_handler.appsync
aws_lambda_powertools.event_handler.content_types
aws_lambda_powertools.event_handler.exceptions
aws_lambda_powertools.event_handler.lambda_function_url
aws_lambda_powertools.event_handler.router

Classes

class ALBResolver (cors: Optional[CORSConfig] = None, debug: Optional[bool] = None, serializer: Optional[Callable[[Dict[~KT, ~VT]], str]] = None, strip_prefixes: Optional[List[str]] = None)

API Gateway and ALB proxy resolver

Examples

Simple example with a custom lambda handler using the Tracer capture_lambda_handler decorator

from aws_lambda_powertools import Tracer
from aws_lambda_powertools.event_handler import APIGatewayRestResolver

tracer = Tracer()
app = APIGatewayRestResolver()

@app.get("/get-call")
def simple_get():
    return {"message": "Foo"}

@app.post("/post-call")
def simple_post():
    post_data: dict = app.current_event.json_body
    return {"message": post_data["value"]}

@tracer.capture_lambda_handler
def lambda_handler(event, context):
    return app.resolve(event, context)

Amazon Application Load Balancer (ALB) resolver

Expand source code 
class ALBResolver(ApiGatewayResolver):
    current_event: ALBEvent

    def __init__(
        self,
        cors: Optional[CORSConfig] = None,
        debug: Optional[bool] = None,
        serializer: Optional[Callable[[Dict], str]] = None,
        strip_prefixes: Optional[List[str]] = None,
    ):
        """Amazon Application Load Balancer (ALB) resolver"""
        super().__init__(ProxyEventType.ALBEvent, cors, debug, serializer, strip_prefixes)

Ancestors

Class variables

var current_event : ALBEvent

Inherited members

class APIGatewayHttpResolver (cors: Optional[CORSConfig] = None, debug: Optional[bool] = None, serializer: Optional[Callable[[Dict[~KT, ~VT]], str]] = None, strip_prefixes: Optional[List[str]] = None)

API Gateway and ALB proxy resolver

Examples

Simple example with a custom lambda handler using the Tracer capture_lambda_handler decorator

from aws_lambda_powertools import Tracer
from aws_lambda_powertools.event_handler import APIGatewayRestResolver

tracer = Tracer()
app = APIGatewayRestResolver()

@app.get("/get-call")
def simple_get():
    return {"message": "Foo"}

@app.post("/post-call")
def simple_post():
    post_data: dict = app.current_event.json_body
    return {"message": post_data["value"]}

@tracer.capture_lambda_handler
def lambda_handler(event, context):
    return app.resolve(event, context)

Amazon API Gateway HTTP API v2 payload resolver

Expand source code 
class APIGatewayHttpResolver(ApiGatewayResolver):
    current_event: APIGatewayProxyEventV2

    def __init__(
        self,
        cors: Optional[CORSConfig] = None,
        debug: Optional[bool] = None,
        serializer: Optional[Callable[[Dict], str]] = None,
        strip_prefixes: Optional[List[str]] = None,
    ):
        """Amazon API Gateway HTTP API v2 payload resolver"""
        super().__init__(ProxyEventType.APIGatewayProxyEventV2, cors, debug, serializer, strip_prefixes)

Ancestors

Class variables

var current_event : APIGatewayProxyEventV2

Inherited members

class APIGatewayRestResolver (cors: Optional[CORSConfig] = None, debug: Optional[bool] = None, serializer: Optional[Callable[[Dict[~KT, ~VT]], str]] = None, strip_prefixes: Optional[List[str]] = None)

API Gateway and ALB proxy resolver

Examples

Simple example with a custom lambda handler using the Tracer capture_lambda_handler decorator

from aws_lambda_powertools import Tracer
from aws_lambda_powertools.event_handler import APIGatewayRestResolver

tracer = Tracer()
app = APIGatewayRestResolver()

@app.get("/get-call")
def simple_get():
    return {"message": "Foo"}

@app.post("/post-call")
def simple_post():
    post_data: dict = app.current_event.json_body
    return {"message": post_data["value"]}

@tracer.capture_lambda_handler
def lambda_handler(event, context):
    return app.resolve(event, context)

Amazon API Gateway REST and HTTP API v1 payload resolver

Expand source code 
class APIGatewayRestResolver(ApiGatewayResolver):
    current_event: APIGatewayProxyEvent

    def __init__(
        self,
        cors: Optional[CORSConfig] = None,
        debug: Optional[bool] = None,
        serializer: Optional[Callable[[Dict], str]] = None,
        strip_prefixes: Optional[List[str]] = None,
    ):
        """Amazon API Gateway REST and HTTP API v1 payload resolver"""
        super().__init__(ProxyEventType.APIGatewayProxyEvent, cors, debug, serializer, strip_prefixes)

    # override route to ignore trailing "/" in routes for REST API
    def route(
        self,
        rule: str,
        method: Union[str, Union[List[str], Tuple[str]]],
        cors: Optional[bool] = None,
        compress: bool = False,
        cache_control: Optional[str] = None,
    ):
        # NOTE: see #1552 for more context.
        return super().route(rule.rstrip("/"), method, cors, compress, cache_control)

    # Override _compile_regex to exclude trailing slashes for route resolution
    @staticmethod
    def _compile_regex(rule: str, base_regex: str = _ROUTE_REGEX):
        return super(APIGatewayRestResolver, APIGatewayRestResolver)._compile_regex(rule, "^{}/*$")

Ancestors

Class variables

var current_event : APIGatewayProxyEvent

Inherited members

class ApiGatewayResolver (proxy_type: enum.Enum = ProxyEventType.APIGatewayProxyEvent, cors: Optional[CORSConfig] = None, debug: Optional[bool] = None, serializer: Optional[Callable[[Dict[~KT, ~VT]], str]] = None, strip_prefixes: Optional[List[str]] = None)

API Gateway and ALB proxy resolver

Examples

Simple example with a custom lambda handler using the Tracer capture_lambda_handler decorator

from aws_lambda_powertools import Tracer
from aws_lambda_powertools.event_handler import APIGatewayRestResolver

tracer = Tracer()
app = APIGatewayRestResolver()

@app.get("/get-call")
def simple_get():
    return {"message": "Foo"}

@app.post("/post-call")
def simple_post():
    post_data: dict = app.current_event.json_body
    return {"message": post_data["value"]}

@tracer.capture_lambda_handler
def lambda_handler(event, context):
    return app.resolve(event, context)

Parameters

proxy_type : ProxyEventType
Proxy request type, defaults to API Gateway V1
cors : CORSConfig
Optionally configure and enabled CORS. Not each route will need to have to cors=True
debug : Optional[bool]
Enables debug mode, by default False. Can be also be enabled by "POWERTOOLS_DEV" environment variable
serializer : Callable, optional
function to serialize obj to a JSON formatted str, by default json.dumps
strip_prefixes : List[str], optional
optional list of prefixes to be removed from the request path before doing the routing. This is often used with api gateways with multiple custom mappings.
Expand source code 
class ApiGatewayResolver(BaseRouter):
    """API Gateway and ALB proxy resolver

    Examples
    --------
    Simple example with a custom lambda handler using the Tracer capture_lambda_handler decorator

    ```python
    from aws_lambda_powertools import Tracer
    from aws_lambda_powertools.event_handler import APIGatewayRestResolver

    tracer = Tracer()
    app = APIGatewayRestResolver()

    @app.get("/get-call")
    def simple_get():
        return {"message": "Foo"}

    @app.post("/post-call")
    def simple_post():
        post_data: dict = app.current_event.json_body
        return {"message": post_data["value"]}

    @tracer.capture_lambda_handler
    def lambda_handler(event, context):
        return app.resolve(event, context)
    ```
    """

    def __init__(
        self,
        proxy_type: Enum = ProxyEventType.APIGatewayProxyEvent,
        cors: Optional[CORSConfig] = None,
        debug: Optional[bool] = None,
        serializer: Optional[Callable[[Dict], str]] = None,
        strip_prefixes: Optional[List[str]] = None,
    ):
        """
        Parameters
        ----------
        proxy_type: ProxyEventType
            Proxy request type, defaults to API Gateway V1
        cors: CORSConfig
            Optionally configure and enabled CORS. Not each route will need to have to cors=True
        debug: Optional[bool]
            Enables debug mode, by default False. Can be also be enabled by "POWERTOOLS_DEV"
            environment variable
        serializer : Callable, optional
            function to serialize `obj` to a JSON formatted `str`, by default json.dumps
        strip_prefixes: List[str], optional
            optional list of prefixes to be removed from the request path before doing the routing. This is often used
            with api gateways with multiple custom mappings.
        """
        self._proxy_type = proxy_type
        self._routes: List[Route] = []
        self._route_keys: List[str] = []
        self._exception_handlers: Dict[Type, Callable] = {}
        self._cors = cors
        self._cors_enabled: bool = cors is not None
        self._cors_methods: Set[str] = {"OPTIONS"}
        self._debug = self._has_debug(debug)
        self._strip_prefixes = strip_prefixes
        self.context: Dict = {}  # early init as customers might add context before event resolution

        # Allow for a custom serializer or a concise json serialization
        self._serializer = serializer or partial(json.dumps, separators=(",", ":"), cls=Encoder)

    def route(
        self,
        rule: str,
        method: Union[str, Union[List[str], Tuple[str]]],
        cors: Optional[bool] = None,
        compress: bool = False,
        cache_control: Optional[str] = None,
    ):
        """Route decorator includes parameter `method`"""

        def register_resolver(func: Callable):
            methods = (method,) if isinstance(method, str) else method
            logger.debug(f"Adding route using rule {rule} and methods: {','.join((m.upper() for m in methods))}")
            if cors is None:
                cors_enabled = self._cors_enabled
            else:
                cors_enabled = cors

            for item in methods:
                self._routes.append(Route(item, self._compile_regex(rule), func, cors_enabled, compress, cache_control))
                route_key = item + rule
                if route_key in self._route_keys:
                    warnings.warn(f"A route like this was already registered. method: '{item}' rule: '{rule}'")
                self._route_keys.append(route_key)
                if cors_enabled:
                    logger.debug(f"Registering method {item.upper()} to Allow Methods in CORS")
                    self._cors_methods.add(item.upper())
            return func

        return register_resolver

    def resolve(self, event, context) -> Dict[str, Any]:
        """Resolves the response based on the provide event and decorator routes

        Parameters
        ----------
        event: Dict[str, Any]
            Event
        context: LambdaContext
            Lambda context
        Returns
        -------
        dict
            Returns the dict response
        """
        if isinstance(event, BaseProxyEvent):
            warnings.warn(
                "You don't need to serialize event to Event Source Data Class when using Event Handler; see issue #1152"
            )
            event = event.raw_event

        if self._debug:
            print(self._json_dump(event))

        # Populate router(s) dependencies without keeping a reference to each registered router
        BaseRouter.current_event = self._to_proxy_event(event)
        BaseRouter.lambda_context = context

        response = self._resolve().build(self.current_event, self._cors)
        self.clear_context()
        return response

    def __call__(self, event, context) -> Any:
        return self.resolve(event, context)

    @staticmethod
    def _has_debug(debug: Optional[bool] = None) -> bool:
        # It might have been explicitly switched off (debug=False)
        if debug is not None:
            return debug

        return powertools_dev_is_set()

    @staticmethod
    def _compile_regex(rule: str, base_regex: str = _ROUTE_REGEX):
        """Precompile regex pattern

        Logic
        -----

        1. Find any dynamic routes defined as <pattern>
            e.g. @app.get("/accounts/<account_id>")
        2. Create a new regex by substituting every dynamic route found as a named group (?P<group>),
        and match whole words only (word boundary) instead of a greedy match

            non-greedy example with word boundary

                rule: '/accounts/<account_id>'
                regex: r'/accounts/(?P<account_id>\\w+\\b)'

                value: /accounts/123/some_other_path
                account_id: 123

            greedy example without word boundary

                regex: r'/accounts/(?P<account_id>.+)'

                value: /accounts/123/some_other_path
                account_id: 123/some_other_path
        3. Compiles a regex and include start (^) and end ($) in between for an exact match

        NOTE: See #520 for context
        """
        rule_regex: str = re.sub(_DYNAMIC_ROUTE_PATTERN, _NAMED_GROUP_BOUNDARY_PATTERN, rule)
        return re.compile(base_regex.format(rule_regex))

    def _to_proxy_event(self, event: Dict) -> BaseProxyEvent:
        """Convert the event dict to the corresponding data class"""
        if self._proxy_type == ProxyEventType.APIGatewayProxyEvent:
            logger.debug("Converting event to API Gateway REST API contract")
            return APIGatewayProxyEvent(event)
        if self._proxy_type == ProxyEventType.APIGatewayProxyEventV2:
            logger.debug("Converting event to API Gateway HTTP API contract")
            return APIGatewayProxyEventV2(event)
        if self._proxy_type == ProxyEventType.LambdaFunctionUrlEvent:
            logger.debug("Converting event to Lambda Function URL contract")
            return LambdaFunctionUrlEvent(event)
        logger.debug("Converting event to ALB contract")
        return ALBEvent(event)

    def _resolve(self) -> ResponseBuilder:
        """Resolves the response or return the not found response"""
        method = self.current_event.http_method.upper()
        path = self._remove_prefix(self.current_event.path)
        for route in self._routes:
            if method != route.method:
                continue
            match_results: Optional[Match] = route.rule.match(path)
            if match_results:
                logger.debug("Found a registered route. Calling function")
                return self._call_route(route, match_results.groupdict())  # pass fn args

        logger.debug(f"No match found for path {path} and method {method}")
        return self._not_found(method)

    def _remove_prefix(self, path: str) -> str:
        """Remove the configured prefix from the path"""
        if not isinstance(self._strip_prefixes, list):
            return path

        for prefix in self._strip_prefixes:
            if path == prefix:
                return "/"
            if self._path_starts_with(path, prefix):
                return path[len(prefix) :]

        return path

    @staticmethod
    def _path_starts_with(path: str, prefix: str):
        """Returns true if the `path` starts with a prefix plus a `/`"""
        if not isinstance(prefix, str) or prefix == "":
            return False

        return path.startswith(prefix + "/")

    def _not_found(self, method: str) -> ResponseBuilder:
        """Called when no matching route was found and includes support for the cors preflight response"""
        headers: Dict[str, Union[str, List[str]]] = {}
        if self._cors:
            logger.debug("CORS is enabled, updating headers.")
            headers.update(self._cors.to_dict())

            if method == "OPTIONS":
                logger.debug("Pre-flight request detected. Returning CORS with null response")
                headers["Access-Control-Allow-Methods"] = ",".join(sorted(self._cors_methods))
                return ResponseBuilder(Response(status_code=204, content_type=None, headers=headers, body=""))

        handler = self._lookup_exception_handler(NotFoundError)
        if handler:
            return ResponseBuilder(handler(NotFoundError()))

        return ResponseBuilder(
            Response(
                status_code=HTTPStatus.NOT_FOUND.value,
                content_type=content_types.APPLICATION_JSON,
                headers=headers,
                body=self._json_dump({"statusCode": HTTPStatus.NOT_FOUND.value, "message": "Not found"}),
            )
        )

    def _call_route(self, route: Route, args: Dict[str, str]) -> ResponseBuilder:
        """Actually call the matching route with any provided keyword arguments."""
        try:
            return ResponseBuilder(self._to_response(route.func(**args)), route)
        except Exception as exc:
            response_builder = self._call_exception_handler(exc, route)
            if response_builder:
                return response_builder

            if self._debug:
                # If the user has turned on debug mode,
                # we'll let the original exception propagate so
                # they get more information about what went wrong.
                return ResponseBuilder(
                    Response(
                        status_code=500,
                        content_type=content_types.TEXT_PLAIN,
                        body="".join(traceback.format_exc()),
                    ),
                    route,
                )

            raise

    def not_found(self, func: Optional[Callable] = None):
        if func is None:
            return self.exception_handler(NotFoundError)
        return self.exception_handler(NotFoundError)(func)

    def exception_handler(self, exc_class: Union[Type[Exception], List[Type[Exception]]]):
        def register_exception_handler(func: Callable):
            if isinstance(exc_class, list):
                for exp in exc_class:
                    self._exception_handlers[exp] = func
            else:
                self._exception_handlers[exc_class] = func
            return func

        return register_exception_handler

    def _lookup_exception_handler(self, exp_type: Type) -> Optional[Callable]:
        # Use "Method Resolution Order" to allow for matching against a base class
        # of an exception
        for cls in exp_type.__mro__:
            if cls in self._exception_handlers:
                return self._exception_handlers[cls]
        return None

    def _call_exception_handler(self, exp: Exception, route: Route) -> Optional[ResponseBuilder]:
        handler = self._lookup_exception_handler(type(exp))
        if handler:
            try:
                return ResponseBuilder(handler(exp), route)
            except ServiceError as service_error:
                exp = service_error

        if isinstance(exp, ServiceError):
            return ResponseBuilder(
                Response(
                    status_code=exp.status_code,
                    content_type=content_types.APPLICATION_JSON,
                    body=self._json_dump({"statusCode": exp.status_code, "message": exp.msg}),
                ),
                route,
            )

        return None

    def _to_response(self, result: Union[Dict, Tuple, Response]) -> Response:
        """Convert the route's result to a Response

         3 main result types are supported:

        - Dict[str, Any]: Rest api response with just the Dict to json stringify and content-type is set to
          application/json
        - Tuple[dict, int]: Same dict handling as above but with the option of including a status code
        - Response: returned as is, and allows for more flexibility
        """
        status_code = HTTPStatus.OK
        if isinstance(result, Response):
            return result
        elif isinstance(result, tuple) and len(result) == 2:
            # Unpack result dict and status code from tuple
            result, status_code = result

        logger.debug("Simple response detected, serializing return before constructing final response")
        return Response(
            status_code=status_code,
            content_type=content_types.APPLICATION_JSON,
            body=self._json_dump(result),
        )

    def _json_dump(self, obj: Any) -> str:
        return self._serializer(obj)

    def include_router(self, router: "Router", prefix: Optional[str] = None) -> None:
        """Adds all routes and context defined in a router

        Parameters
        ----------
        router : Router
            The Router containing a list of routes to be registered after the existing routes
        prefix : str, optional
            An optional prefix to be added to the originally defined rule
        """

        # Add reference to parent ApiGatewayResolver to support use cases where people subclass it to add custom logic
        router.api_resolver = self

        # Merge app and router context
        self.context.update(**router.context)
        # use pointer to allow context clearance after event is processed e.g., resolve(evt, ctx)
        router.context = self.context

        for route, func in router._routes.items():
            if prefix:
                rule = route[0]
                rule = prefix if rule == "/" else f"{prefix}{rule}"
                route = (rule, *route[1:])

            self.route(*route)(func)

Ancestors

Subclasses

Class variables

var context : dict
var current_event : BaseProxyEvent
var lambda_context : LambdaContext

Methods

def exception_handler(self, exc_class: Union[Type[Exception], List[Type[Exception]]])
Expand source code 
def exception_handler(self, exc_class: Union[Type[Exception], List[Type[Exception]]]):
    def register_exception_handler(func: Callable):
        if isinstance(exc_class, list):
            for exp in exc_class:
                self._exception_handlers[exp] = func
        else:
            self._exception_handlers[exc_class] = func
        return func

    return register_exception_handler
def include_router(self, router: Router, prefix: Optional[str] = None) ‑> None

Adds all routes and context defined in a router

Parameters

router : Router
The Router containing a list of routes to be registered after the existing routes
prefix : str, optional
An optional prefix to be added to the originally defined rule
Expand source code 
def include_router(self, router: "Router", prefix: Optional[str] = None) -> None:
    """Adds all routes and context defined in a router

    Parameters
    ----------
    router : Router
        The Router containing a list of routes to be registered after the existing routes
    prefix : str, optional
        An optional prefix to be added to the originally defined rule
    """

    # Add reference to parent ApiGatewayResolver to support use cases where people subclass it to add custom logic
    router.api_resolver = self

    # Merge app and router context
    self.context.update(**router.context)
    # use pointer to allow context clearance after event is processed e.g., resolve(evt, ctx)
    router.context = self.context

    for route, func in router._routes.items():
        if prefix:
            rule = route[0]
            rule = prefix if rule == "/" else f"{prefix}{rule}"
            route = (rule, *route[1:])

        self.route(*route)(func)
def not_found(self, func: Optional[Callable] = None)
Expand source code 
def not_found(self, func: Optional[Callable] = None):
    if func is None:
        return self.exception_handler(NotFoundError)
    return self.exception_handler(NotFoundError)(func)
def resolve(self, event, context) ‑> Dict[str, Any]

Resolves the response based on the provide event and decorator routes

Parameters

event : Dict[str, Any]
Event
context : LambdaContext
Lambda context

Returns

dict
Returns the dict response
Expand source code 
def resolve(self, event, context) -> Dict[str, Any]:
    """Resolves the response based on the provide event and decorator routes

    Parameters
    ----------
    event: Dict[str, Any]
        Event
    context: LambdaContext
        Lambda context
    Returns
    -------
    dict
        Returns the dict response
    """
    if isinstance(event, BaseProxyEvent):
        warnings.warn(
            "You don't need to serialize event to Event Source Data Class when using Event Handler; see issue #1152"
        )
        event = event.raw_event

    if self._debug:
        print(self._json_dump(event))

    # Populate router(s) dependencies without keeping a reference to each registered router
    BaseRouter.current_event = self._to_proxy_event(event)
    BaseRouter.lambda_context = context

    response = self._resolve().build(self.current_event, self._cors)
    self.clear_context()
    return response
def route(self, rule: str, method: Union[str, List[str], Tuple[str]], cors: Optional[bool] = None, compress: bool = False, cache_control: Optional[str] = None)

Route decorator includes parameter method

Expand source code 
def route(
    self,
    rule: str,
    method: Union[str, Union[List[str], Tuple[str]]],
    cors: Optional[bool] = None,
    compress: bool = False,
    cache_control: Optional[str] = None,
):
    """Route decorator includes parameter `method`"""

    def register_resolver(func: Callable):
        methods = (method,) if isinstance(method, str) else method
        logger.debug(f"Adding route using rule {rule} and methods: {','.join((m.upper() for m in methods))}")
        if cors is None:
            cors_enabled = self._cors_enabled
        else:
            cors_enabled = cors

        for item in methods:
            self._routes.append(Route(item, self._compile_regex(rule), func, cors_enabled, compress, cache_control))
            route_key = item + rule
            if route_key in self._route_keys:
                warnings.warn(f"A route like this was already registered. method: '{item}' rule: '{rule}'")
            self._route_keys.append(route_key)
            if cors_enabled:
                logger.debug(f"Registering method {item.upper()} to Allow Methods in CORS")
                self._cors_methods.add(item.upper())
        return func

    return register_resolver

Inherited members

class AppSyncResolver

AppSync resolver decorator

Example

Sample usage

from aws_lambda_powertools.event_handler import AppSyncResolver

app = AppSyncResolver()

@app.resolver(type_name="Query", field_name="listLocations")
def list_locations(page: int = 0, size: int = 10) -> list:
    # Your logic to fetch locations with arguments passed in
    return [{"id": 100, "name": "Smooth Grooves"}]

@app.resolver(type_name="Merchant", field_name="extraInfo")
def get_extra_info() -> dict:
    # Can use "app.current_event.source" to filter within the parent context
    account_type = app.current_event.source["accountType"]
    method = "BTC" if account_type == "NEW" else "USD"
    return {"preferredPaymentMethod": method}

@app.resolver(field_name="commonField")
def common_field() -> str:
    # Would match all fieldNames matching 'commonField'
    return str(uuid.uuid4())
Expand source code 
class AppSyncResolver(BaseRouter):
    """
    AppSync resolver decorator

    Example
    -------

    **Sample usage**

        from aws_lambda_powertools.event_handler import AppSyncResolver

        app = AppSyncResolver()

        @app.resolver(type_name="Query", field_name="listLocations")
        def list_locations(page: int = 0, size: int = 10) -> list:
            # Your logic to fetch locations with arguments passed in
            return [{"id": 100, "name": "Smooth Grooves"}]

        @app.resolver(type_name="Merchant", field_name="extraInfo")
        def get_extra_info() -> dict:
            # Can use "app.current_event.source" to filter within the parent context
            account_type = app.current_event.source["accountType"]
            method = "BTC" if account_type == "NEW" else "USD"
            return {"preferredPaymentMethod": method}

        @app.resolver(field_name="commonField")
        def common_field() -> str:
            # Would match all fieldNames matching 'commonField'
            return str(uuid.uuid4())
    """

    def __init__(self):
        super().__init__()
        self.context = {}  # early init as customers might add context before event resolution

    def resolve(
        self, event: dict, context: LambdaContext, data_model: Type[AppSyncResolverEvent] = AppSyncResolverEvent
    ) -> Any:
        """Resolve field_name

        Parameters
        ----------
        event : dict
            Lambda event
        context : LambdaContext
            Lambda context
        data_model:
            Your data data_model to decode AppSync event, by default AppSyncResolverEvent

        Example
        -------

        ```python
        from aws_lambda_powertools.event_handler import AppSyncResolver
        from aws_lambda_powertools.utilities.typing import LambdaContext

        @app.resolver(field_name="createSomething")
        def create_something(id: str):  # noqa AA03 VNE003
            return id

        def handler(event, context: LambdaContext):
            return app.resolve(event, context)
        ```

        **Bringing custom models**

        ```python
        from aws_lambda_powertools import Logger, Tracer

        from aws_lambda_powertools.logging import correlation_paths
        from aws_lambda_powertools.event_handler import AppSyncResolver

        tracer = Tracer(service="sample_resolver")
        logger = Logger(service="sample_resolver")
        app = AppSyncResolver()


        class MyCustomModel(AppSyncResolverEvent):
            @property
            def country_viewer(self) -> str:
                return self.request_headers.get("cloudfront-viewer-country")


        @app.resolver(field_name="listLocations")
        @app.resolver(field_name="locations")
        def get_locations(name: str, description: str = ""):
            if app.current_event.country_viewer == "US":
                ...
            return name + description


        @logger.inject_lambda_context(correlation_id_path=correlation_paths.APPSYNC_RESOLVER)
        @tracer.capture_lambda_handler
        def lambda_handler(event, context):
            return app.resolve(event, context, data_model=MyCustomModel)
        ```

        Returns
        -------
        Any
            Returns the result of the resolver

        Raises
        -------
        ValueError
            If we could not find a field resolver
        """
        # Maintenance: revisit generics/overload to fix [attr-defined] in mypy usage
        BaseRouter.current_event = data_model(event)
        BaseRouter.lambda_context = context

        resolver = self._get_resolver(BaseRouter.current_event.type_name, BaseRouter.current_event.field_name)
        response = resolver(**BaseRouter.current_event.arguments)
        self.clear_context()

        return response

    def _get_resolver(self, type_name: str, field_name: str) -> Callable:
        """Get resolver for field_name

        Parameters
        ----------
        type_name : str
            Type name
        field_name : str
            Field name

        Returns
        -------
        Callable
            callable function and configuration
        """
        full_name = f"{type_name}.{field_name}"
        resolver = self._resolvers.get(full_name, self._resolvers.get(f"*.{field_name}"))
        if not resolver:
            raise ValueError(f"No resolver found for '{full_name}'")
        return resolver["func"]

    def __call__(
        self, event: dict, context: LambdaContext, data_model: Type[AppSyncResolverEvent] = AppSyncResolverEvent
    ) -> Any:
        """Implicit lambda handler which internally calls `resolve`"""
        return self.resolve(event, context, data_model)

    def include_router(self, router: "Router") -> None:
        """Adds all resolvers defined in a router

        Parameters
        ----------
        router : Router
            A router containing a dict of field resolvers
        """
        # Merge app and router context
        self.context.update(**router.context)
        # use pointer to allow context clearance after event is processed e.g., resolve(evt, ctx)
        router.context = self.context

        self._resolvers.update(router._resolvers)

Ancestors

Class variables

var context : dict
var current_event : ~AppSyncResolverEventT
var lambda_context : LambdaContext

Methods

def include_router(self, router: Router) ‑> None

Adds all resolvers defined in a router

Parameters

router : Router
A router containing a dict of field resolvers
Expand source code 
def include_router(self, router: "Router") -> None:
    """Adds all resolvers defined in a router

    Parameters
    ----------
    router : Router
        A router containing a dict of field resolvers
    """
    # Merge app and router context
    self.context.update(**router.context)
    # use pointer to allow context clearance after event is processed e.g., resolve(evt, ctx)
    router.context = self.context

    self._resolvers.update(router._resolvers)
def resolve(self, event: dict, context: LambdaContext, data_model: Type[AppSyncResolverEvent] = aws_lambda_powertools.utilities.data_classes.appsync_resolver_event.AppSyncResolverEvent) ‑> Any

Resolve field_name

Parameters

event : dict
Lambda event
context : LambdaContext
Lambda context

data_model: Your data data_model to decode AppSync event, by default AppSyncResolverEvent

Example

from aws_lambda_powertools.event_handler import AppSyncResolver
from aws_lambda_powertools.utilities.typing import LambdaContext

@app.resolver(field_name="createSomething")
def create_something(id: str):  # noqa AA03 VNE003
    return id

def handler(event, context: LambdaContext):
    return app.resolve(event, context)

Bringing custom models

from aws_lambda_powertools import Logger, Tracer

from aws_lambda_powertools.logging import correlation_paths
from aws_lambda_powertools.event_handler import AppSyncResolver

tracer = Tracer(service="sample_resolver")
logger = Logger(service="sample_resolver")
app = AppSyncResolver()


class MyCustomModel(AppSyncResolverEvent):
    @property
    def country_viewer(self) -> str:
        return self.request_headers.get("cloudfront-viewer-country")


@app.resolver(field_name="listLocations")
@app.resolver(field_name="locations")
def get_locations(name: str, description: str = ""):
    if app.current_event.country_viewer == "US":
        ...
    return name + description


@logger.inject_lambda_context(correlation_id_path=correlation_paths.APPSYNC_RESOLVER)
@tracer.capture_lambda_handler
def lambda_handler(event, context):
    return app.resolve(event, context, data_model=MyCustomModel)

Returns

Any
Returns the result of the resolver

Raises

ValueError
If we could not find a field resolver
Expand source code 
def resolve(
    self, event: dict, context: LambdaContext, data_model: Type[AppSyncResolverEvent] = AppSyncResolverEvent
) -> Any:
    """Resolve field_name

    Parameters
    ----------
    event : dict
        Lambda event
    context : LambdaContext
        Lambda context
    data_model:
        Your data data_model to decode AppSync event, by default AppSyncResolverEvent

    Example
    -------

    ```python
    from aws_lambda_powertools.event_handler import AppSyncResolver
    from aws_lambda_powertools.utilities.typing import LambdaContext

    @app.resolver(field_name="createSomething")
    def create_something(id: str):  # noqa AA03 VNE003
        return id

    def handler(event, context: LambdaContext):
        return app.resolve(event, context)
    ```

    **Bringing custom models**

    ```python
    from aws_lambda_powertools import Logger, Tracer

    from aws_lambda_powertools.logging import correlation_paths
    from aws_lambda_powertools.event_handler import AppSyncResolver

    tracer = Tracer(service="sample_resolver")
    logger = Logger(service="sample_resolver")
    app = AppSyncResolver()


    class MyCustomModel(AppSyncResolverEvent):
        @property
        def country_viewer(self) -> str:
            return self.request_headers.get("cloudfront-viewer-country")


    @app.resolver(field_name="listLocations")
    @app.resolver(field_name="locations")
    def get_locations(name: str, description: str = ""):
        if app.current_event.country_viewer == "US":
            ...
        return name + description


    @logger.inject_lambda_context(correlation_id_path=correlation_paths.APPSYNC_RESOLVER)
    @tracer.capture_lambda_handler
    def lambda_handler(event, context):
        return app.resolve(event, context, data_model=MyCustomModel)
    ```

    Returns
    -------
    Any
        Returns the result of the resolver

    Raises
    -------
    ValueError
        If we could not find a field resolver
    """
    # Maintenance: revisit generics/overload to fix [attr-defined] in mypy usage
    BaseRouter.current_event = data_model(event)
    BaseRouter.lambda_context = context

    resolver = self._get_resolver(BaseRouter.current_event.type_name, BaseRouter.current_event.field_name)
    response = resolver(**BaseRouter.current_event.arguments)
    self.clear_context()

    return response

Inherited members

class CORSConfig (allow_origin: str = '*', allow_headers: Optional[List[str]] = None, expose_headers: Optional[List[str]] = None, max_age: Optional[int] = None, allow_credentials: bool = False)

CORS Config

Examples

Simple cors example using the default permissive cors, not this should only be used during early prototyping

from aws_lambda_powertools.event_handler import APIGatewayRestResolver

app = APIGatewayRestResolver()

@app.get("/my/path", cors=True)
def with_cors():
    return {"message": "Foo"}

Using a custom CORSConfig where with_cors used the custom provided CORSConfig and without_cors do not include any cors headers.

from aws_lambda_powertools.event_handler.api_gateway import (
    APIGatewayRestResolver, CORSConfig
)

cors_config = CORSConfig(
    allow_origin="https://wwww.example.com/",
    expose_headers=["x-exposed-response-header"],
    allow_headers=["x-custom-request-header"],
    max_age=100,
    allow_credentials=True,
)
app = APIGatewayRestResolver(cors=cors_config)

@app.get("/my/path")
def with_cors():
    return {"message": "Foo"}

@app.get("/another-one", cors=False)
def without_cors():
    return {"message": "Foo"}

Parameters

allow_origin : str
The value of the Access-Control-Allow-Origin to send in the response. Defaults to "*", but should only be used during development.
allow_headers : Optional[List[str]]
The list of additional allowed headers. This list is added to list of built-in allowed headers: Authorization, Content-Type, X-Amz-Date, X-Api-Key, X-Amz-Security-Token.
expose_headers : Optional[List[str]]
A list of values to return for the Access-Control-Expose-Headers
max_age : Optional[int]
The value for the Access-Control-Max-Age
allow_credentials : bool
A boolean value that sets the value of Access-Control-Allow-Credentials
Expand source code 
class CORSConfig:
    """CORS Config

    Examples
    --------

    Simple cors example using the default permissive cors, not this should only be used during early prototyping

    ```python
    from aws_lambda_powertools.event_handler import APIGatewayRestResolver

    app = APIGatewayRestResolver()

    @app.get("/my/path", cors=True)
    def with_cors():
        return {"message": "Foo"}
    ```

    Using a custom CORSConfig where `with_cors` used the custom provided CORSConfig and `without_cors`
    do not include any cors headers.

    ```python
    from aws_lambda_powertools.event_handler.api_gateway import (
        APIGatewayRestResolver, CORSConfig
    )

    cors_config = CORSConfig(
        allow_origin="https://wwww.example.com/",
        expose_headers=["x-exposed-response-header"],
        allow_headers=["x-custom-request-header"],
        max_age=100,
        allow_credentials=True,
    )
    app = APIGatewayRestResolver(cors=cors_config)

    @app.get("/my/path")
    def with_cors():
        return {"message": "Foo"}

    @app.get("/another-one", cors=False)
    def without_cors():
        return {"message": "Foo"}
    ```
    """

    _REQUIRED_HEADERS = ["Authorization", "Content-Type", "X-Amz-Date", "X-Api-Key", "X-Amz-Security-Token"]

    def __init__(
        self,
        allow_origin: str = "*",
        allow_headers: Optional[List[str]] = None,
        expose_headers: Optional[List[str]] = None,
        max_age: Optional[int] = None,
        allow_credentials: bool = False,
    ):
        """
        Parameters
        ----------
        allow_origin: str
            The value of the `Access-Control-Allow-Origin` to send in the response. Defaults to "*", but should
            only be used during development.
        allow_headers: Optional[List[str]]
            The list of additional allowed headers. This list is added to list of
            built-in allowed headers: `Authorization`, `Content-Type`, `X-Amz-Date`,
            `X-Api-Key`, `X-Amz-Security-Token`.
        expose_headers: Optional[List[str]]
            A list of values to return for the Access-Control-Expose-Headers
        max_age: Optional[int]
            The value for the `Access-Control-Max-Age`
        allow_credentials: bool
            A boolean value that sets the value of `Access-Control-Allow-Credentials`
        """
        self.allow_origin = allow_origin
        self.allow_headers = set(self._REQUIRED_HEADERS + (allow_headers or []))
        self.expose_headers = expose_headers or []
        self.max_age = max_age
        self.allow_credentials = allow_credentials

    def to_dict(self) -> Dict[str, str]:
        """Builds the configured Access-Control http headers"""
        headers: Dict[str, str] = {
            "Access-Control-Allow-Origin": self.allow_origin,
            "Access-Control-Allow-Headers": ",".join(sorted(self.allow_headers)),
        }

        if self.expose_headers:
            headers["Access-Control-Expose-Headers"] = ",".join(self.expose_headers)
        if self.max_age is not None:
            headers["Access-Control-Max-Age"] = str(self.max_age)
        if self.allow_credentials is True:
            headers["Access-Control-Allow-Credentials"] = "true"
        return headers

Methods

def to_dict(self) ‑> Dict[str, str]

Builds the configured Access-Control http headers

Expand source code 
def to_dict(self) -> Dict[str, str]:
    """Builds the configured Access-Control http headers"""
    headers: Dict[str, str] = {
        "Access-Control-Allow-Origin": self.allow_origin,
        "Access-Control-Allow-Headers": ",".join(sorted(self.allow_headers)),
    }

    if self.expose_headers:
        headers["Access-Control-Expose-Headers"] = ",".join(self.expose_headers)
    if self.max_age is not None:
        headers["Access-Control-Max-Age"] = str(self.max_age)
    if self.allow_credentials is True:
        headers["Access-Control-Allow-Credentials"] = "true"
    return headers
class LambdaFunctionUrlResolver (cors: Optional[CORSConfig] = None, debug: Optional[bool] = None, serializer: Optional[Callable[[Dict[~KT, ~VT]], str]] = None, strip_prefixes: Optional[List[str]] = None)

AWS Lambda Function URL resolver

Notes:

Lambda Function URL follows the API Gateway HTTP APIs Payload Format Version 2.0.

Documentation: - https://docs.aws.amazon.com/lambda/latest/dg/urls-configuration.html - https://docs.aws.amazon.com/lambda/latest/dg/urls-invocation.html#urls-payloads

Examples

Simple example integrating with Tracer

```python from aws_lambda_powertools import Tracer from aws_lambda_powertools.event_handler import LambdaFunctionUrlResolver

tracer = Tracer() app = LambdaFunctionUrlResolver()

@app.get("/get-call") def simple_get(): return {"message": "Foo"}

@app.post("/post-call") def simple_post(): post_data: dict = app.current_event.json_body return {"message": post_data}

@tracer.capture_lambda_handler def lambda_handler(event, context): return app.resolve(event, context)

Parameters

proxy_type : ProxyEventType
Proxy request type, defaults to API Gateway V1
cors : CORSConfig
Optionally configure and enabled CORS. Not each route will need to have to cors=True
debug : Optional[bool]
Enables debug mode, by default False. Can be also be enabled by "POWERTOOLS_DEV" environment variable
serializer : Callable, optional
function to serialize obj to a JSON formatted str, by default json.dumps
strip_prefixes : List[str], optional
optional list of prefixes to be removed from the request path before doing the routing. This is often used with api gateways with multiple custom mappings.
Expand source code 
class LambdaFunctionUrlResolver(ApiGatewayResolver):
    """AWS Lambda Function URL resolver

    Notes:
    -----
    Lambda Function URL follows the API Gateway HTTP APIs Payload Format Version 2.0.

    Documentation:
    - https://docs.aws.amazon.com/lambda/latest/dg/urls-configuration.html
    - https://docs.aws.amazon.com/lambda/latest/dg/urls-invocation.html#urls-payloads

    Examples
    --------
    Simple example integrating with Tracer

    ```python
    from aws_lambda_powertools import Tracer
    from aws_lambda_powertools.event_handler import LambdaFunctionUrlResolver

    tracer = Tracer()
    app = LambdaFunctionUrlResolver()

    @app.get("/get-call")
    def simple_get():
        return {"message": "Foo"}

    @app.post("/post-call")
    def simple_post():
        post_data: dict = app.current_event.json_body
        return {"message": post_data}

    @tracer.capture_lambda_handler
    def lambda_handler(event, context):
        return app.resolve(event, context)
    """

    current_event: LambdaFunctionUrlEvent

    def __init__(
        self,
        cors: Optional[CORSConfig] = None,
        debug: Optional[bool] = None,
        serializer: Optional[Callable[[Dict], str]] = None,
        strip_prefixes: Optional[List[str]] = None,
    ):
        super().__init__(ProxyEventType.LambdaFunctionUrlEvent, cors, debug, serializer, strip_prefixes)

Ancestors

Class variables

var current_event : LambdaFunctionUrlEvent

Inherited members

class Response (status_code: int, content_type: Optional[str] = None, body: Union[str, bytes, None] = None, headers: Optional[Dict[str, Union[str, List[str]]]] = None, cookies: Optional[List[Cookie]] = None)

Response data class that provides greater control over what is returned from the proxy event

Parameters

status_code : int
Http status code, example 200
content_type : str
Optionally set the Content-Type header, example "application/json". Note this will be merged into any provided http headers
body : Union[str, bytes, None]
Optionally set the response body. Note: bytes body will be automatically base64 encoded
headers : dict[str, Union[str, List[str]]]
Optionally set specific http headers. Setting "Content-Type" here would override the content_type value.
cookies : list[Cookie]
Optionally set cookies.
Expand source code 
class Response:
    """Response data class that provides greater control over what is returned from the proxy event"""

    def __init__(
        self,
        status_code: int,
        content_type: Optional[str] = None,
        body: Union[str, bytes, None] = None,
        headers: Optional[Dict[str, Union[str, List[str]]]] = None,
        cookies: Optional[List[Cookie]] = None,
    ):
        """

        Parameters
        ----------
        status_code: int
            Http status code, example 200
        content_type: str
            Optionally set the Content-Type header, example "application/json". Note this will be merged into any
            provided http headers
        body: Union[str, bytes, None]
            Optionally set the response body. Note: bytes body will be automatically base64 encoded
        headers: dict[str, Union[str, List[str]]]
            Optionally set specific http headers. Setting "Content-Type" here would override the `content_type` value.
        cookies: list[Cookie]
            Optionally set cookies.
        """
        self.status_code = status_code
        self.body = body
        self.base64_encoded = False
        self.headers: Dict[str, Union[str, List[str]]] = headers if headers else {}
        self.cookies = cookies or []
        if content_type:
            self.headers.setdefault("Content-Type", content_type)